Yet more fly cutter questions

This topic has 7 replies, 6 voices, and was last updated 16 February 2021 at 10:26 by JasonB.

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16 February 2021 at 08:16 #527646
Chris Chadwick
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@chrischadwick43059
I've just started to rough out a fly cutter body to help me rough out material to size on my new milling machine. As end mils are expensive.

I will be adding a 10 degree face to the end face of the body, then my understanding of the design is I need to mill a slot for a tool holder with one face on the centerline to put the tip of the tool on "centre height".

If this is true, then why do all the bought fly cutters have the locking screws for the tool on the top side of the tool, so pushing the tool, unless a good fit in the slot below centre height?

I was planning to put my screws onto the bottom of the tool to push the tool up to centre height, even with smaller tools than the slot.

What am I missing, or does this make sense?

Is it that the centre height isn't so important, and that the screws below aren't as solid as the main body?
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16 February 2021 at 08:16 #20159
Chris Chadwick
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@chrischadwick43059
16 February 2021 at 08:38 #527651
pgk pgk
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@pgkpgk17461
I'm confused. Height is determined by the quill. Having the tool face on the centre-line of rotation is probably beneficial but that could be angle ground even if a bar of HSS was offset from centre (assuming you use HSS).

The commercial flycutter i have has such a slot so the HSS angles downwards and is held in the slot by horizontal grub screws. A simpler DIY one I made using a round insert has it mounted on a straight bar such that the cutting edge is on the diameter of rotation. Other designs can be as simple as a disc with a hole for a vertical HSS cutter held by a grub-screw (and ground appropriately)…

pgk
16 February 2021 at 08:47 #527652
Martin Connelly
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@martinconnelly55370
The aim of the design is to have the cutting edge at the point of maximum radius. Anywhere other than with the cutting tip in line with the spindle's centre of rotation causes issues with clearance behind the cutting point and also changes the angle the cutting point meets the workpiece. All the fly cutters have locking screws on the side to push the tool against the side that is in line with the spindle's rotation. Are you mixing up top and side views?

Have you looked at any YouTube videos on making them, they are pretty clear on the design?

Martin C
16 February 2021 at 08:53 #527654
Mike Crossfield
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@mikecrossfield92481
Chris,

Not a sound arrangement to take the cutting forces on the tips of the clamping screws. If the HSS does not fill the slot, and you’re worried about the tool top face being on centre line, just add packing underneath.

Mike
16 February 2021 at 09:37 #527667
Chris Chadwick
Participant
@chrischadwick43059
pgk, By height I was meaning looking on the end of the cutter. I imagined it like a lathe boring tool. The cutting face is on the tool centre.

Martin, I''ve seen that video, and if you watch part 2 also you will see at the end her clamping screws are to the underside of the tool blank. I hadn't noticed that before.

Mike, I agree, hence my question. Maybe due to the reasonablt large diameter the tool centre height isn't as important. like when turning. If you are turning 50 dia, it isn't as important as 5 dia

I think I might just add screw holes on both sides of the tool and see how it goes as to which ones I end up using.
16 February 2021 at 09:39 #527668
David George 1
Participant
@davidgeorge1
This is my favourite fly cutter made from a piece of 1 inch silver steel with a 1/2 inch stem. It has a piece of HSS toolsteel held by a grub screw. I also have a piece of diamiter carbide for hard materials easily sharpened and fitts in to collet set etc.

David
16 February 2021 at 10:26 #527684
JasonB
Moderator
@jasonb
The screws should bear on the "top" of the tool so that it is held against a solid surface just like it is when in a lathe.

If you have the screws against the bottom then there is less support for the cutting forces as they go through the tool and also as the screw is back from the edge you effectively get more "overhang"
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